A method of powder making by impacting or otherwise breaking a metal or alloy liquid into fine droplets with a rapidly moving fluid (atomizing medium), followed by condensation into a solid powder.

Introduction

A method of powder making by impacting or otherwise breaking a metal or alloy liquid into fine droplets with a rapidly moving fluid (atomizing medium), followed by condensation into a solid powder. Atomization is the best way to produce fully alloyed powder, and its product is called pre-alloyed powder. Not only does each particle of the powder have exactly the same chemical composition as the intended molten alloy, but the crystalline structure is refined due to rapid solidification; the macrosegregation of the second phase is eliminated.

The most widely used are aerosolization and water atomization methods. Atomizing pulverizing, the metal raw material is melted into an alloy liquid (generally overheat 100-150 ° C) by electric furnace or induction furnace, and then injected into the tundish located above the atomizing nozzle. The alloy liquid flows out from the bottom of the tundish through the leaky hole and meets with the high-speed airflow or water flow through the nozzle to be atomized into small droplets. The atomized droplets quickly solidify into the alloy powder in the closed atomization barrel. In general, inert gas atomized powder particles are rounded and have the lowest oxygen content (less than l00x10), which can be directly densified using hot forming techniques such as hot isostatic pressing. Water atomized powder particles are mostly irregular shape, high oxygen content (higher than 600 × 10), to be annealed, but it has good compressibility, cold forming, and then sintered into mechanical parts. The atomization milling method is easy to mass production, but due to the alloy liquid and slag body and refractory crucible contact, inevitably bring in the preparation of non-metallic inclusions in the powder. Therefore, according to the ESR principle, Soderfors Powder Company of Sweden first changed the tundish with a capacity of 7 t into an ESG device. The nitrogen atomized high-speed steel powder in non-nitrogen The amount of metal inclusions reduced to the original amount of 1/10, ASP powder high-speed steel bending strength increased from 3500MPa to 4000MPa above.